Mechanical seal assemblies are conventionally utilized on fluid handling equipment such as pumps and the like which are utilized in conjunction with highly corrosive and/or high temperature fluids, such as chemicals, petro-chemicals, steam and the like. The seal assemblies, in their most common mode of usage, are of the "inside" type in that the seal assembly is positioned in surrounding relationship to a rotatable shaft and is disposed within a recess formed in the surrounding housing (commonly referred to as the stuffing box). A stationary gland is conventionally positioned adjacent the outer end of the recess and is fixedly secured to the stuffing box, as by screws. The gland nonrotatably mounts thereon the stationary annular seal member (commonly referred to as the gland insert), which insert supports the nonrotatable seal face ring. To prevent leakage between the gland and the gland insert, an annular packing is provided therebetween.
In many conventional use applications, the mechanical seal is a double assembly in that one seal assembly is disposed adjacent the outer end of the stuffing box for cooperation with the gland, as described above, and a further seal assembly is disposed adjacent the inner end of the stuffing box. This inner seal assembly is of substantially the same construction as the outer seal assembly except that the stationary seal ring (the insert) is seated on the stuffing box, and a packing ring is provided therebetween to prevent leakage from occurring around the outer periphery of the insert.
The packing which is provided between the insert and the gland, or between the insert and the stuffing box, has throughout the years assumed many different configurations and utilized many different materials. In situations where the seal assembly is used in conjunction with noncorrosive or low temperature fluids, then the packing is normally of an elastomeric material having a conventional cross section, such as an O-ring. These use conditions have not created any serious problem relative to installation or use.
However, in use situations where the seal assembly is exposed to corrosive and/or high temperature fluids, elastomers can not be used for the packing, and hence other materials such as Teflon and graphite have been utilized in view of their ability to withstand exposure to the corrosive and/or high temperature fluids. Packing rings constructed of these materials, however, are much more difficult to handle during installation since these materials are relatively rigid and/or inelastic. While they do permit very limited compression, nevertheless packings of these materials do not function like elastomers. Hence, installation of these packings, and hence installation of the mechanical seal assembly, has been a long-standing problem.
More specifically, mechanical seal assemblies are normally installed on the equipment at the job site, and hence installation of the mechanical seal assembly into the stuffing box of the apparatus is essentially a manual operation since not only is the recess within the stuffing box of small dimensions, but the job-site installation prevents utilization of automated or other factory-type equipment for assisting in installation, particularly when press fits are utilized. Hence, when installing a mechanical seal at the inner end of the stuffing box, the installation of the insert, and particularly the positioning of the packing between the stuffing box and the insert, has long been a problem. Because of the length of the stuffing box recess, and the required manual installation of the insert and packing ring, use of a heavy press or interference fit is impossible. Further, the packing often comprises some type of spreader ring arrangement, such as an outer V-shaped Teflon ring having a tapered spreader block inserted therein for effecting expansion of the V-shaped ring into sealing engagement at inner and outer diameters. This type of spreader ring arrangement can be manually installed but does not exert any sufficient holding force. Hence, tilting of the insert relative to the stuffing box, during the installation procedure, has been a long-standing problem.
Similar installation problems are also encountered when the mechanical seal assembly is mounted in a vertical orientation, such as on a mixer shaft or the like, and the gland is disposed uppermost. When a mechanical seal assembly is installed at a job site in a vertical orientation, the installation is again manually performed and the seal components are fitted vertically downwardly over the shaft into the stuffing box. The packing ring, such as the V-ring and spreader, or a graphite packing ring, is manually fitted into the gland, and the insert is then manually fitted into the packing ring. This assembly operation can be manually performed since the insert rests on top of the gland. To then mount the gland and insert onto the apparatus, the installer must turn the gland-insert subassembly upside down so that the insert is directed downwardly, whereupon this subassembly is then vertically moved downwardly over the shaft into position within the stuffing box. During this downward vertical installation, however, the installer must manually hold the insert into the gland or else it will fall out. Needless to say, when the installer can no longer grip the insert, such as when the subassembly is positioned closely adjacent the stuffing box, then often the insert falls out of the gland, prior to proper seating of the subassembly on the stuffing box. This often results in tilting, which prevents proper sealing engagement between the gland and insert.
In an attempt to prevent separation between the gland and insert, such as for vertical installations, others have attempted for many years to utilize Teflon packing rings having a heavy rectangular cross section, which packing ring has a heavy press or interference fit between its radially inner and outer surfaces with the insert and gland, respectively. These arrangements, however, can not be successfully and repetitively manually assembled at the job site in view of the excessive axial pressure force (i.e., approximately 50 to 100 pounds) required to create the interference fits. Further, this arrangement relies on these heavy press fits to create seal areas adjacent the radially inner and outer surfaces of the packing ring.
Accordingly, all of the known packing arrangements as used between the insert and the gland or stuffing box have necessarily resulted in long-standing installation problems and/or have prevented or interfered with the necessary manual assembly and installation of the seal assembly at the job site.
Further, most of these known packings have also relied on radial compression of the packing between the insert and gland (or stuffing box) for creating seal areas adjacent the radially inner and outer walls of the packing. Reliance on these radially inner and outer walls for creating seal areas necessarily increases the required pressure between these walls, which in turn interferes with the successful manual assembly of the insert-gland (or stuffing box) subassembly.
Many of the prior packings, and the problems associated therewith, are explained in greater detail hereinafter with reference to the accompanying drawings.
Accordingly, it is an object of this invention to provide an improved packing for a mechanical seal, specifically a packing which coacts between the insert and the gland or stuffing box, which packing is usable for corrosive and/or high temperature fluids and greatly facilitates manual assembly and installation of the seal assembly into the stuffing box, both in a vertical and a horizontal orientation, and hence overcomes the many disadvantages associated with prior packings.
More specifically, it is an object of this invention to provide an improved packing which coacts between the insert and the gland or stuffing box, which packing is a Teflon ring having a substantially rectangular cross section. The ring on the radially outer periphery thereof is provided with an encircling rib which is integral therewith and projects radially outwardly thereof. This rib creates an interference or press fit with an internal annular wall formed on the gland or stuffing box to permit the packing ring and the gland or stuffing box to be securely locked together, while at the same time enabling this pressure fit to be accomplished manually at the job site using only light finger pressure (i.e., an axial pressure force of up to approximately 10 pounds) for effecting the assembly. This can hence be easily accomplished, and can be uniformly applied around the ring to avoid distortion thereof. The packing ring also has the radially inner periphery thereof maintained in engagement with the insert by means of a light pressure or interference fit. This arrangement, when installed, is subject to axial compression such that opposite axial end faces of the packing ring seat on confronting faces on the insert and gland (or stuffing box) to create seal areas at the axial end faces, rather than at the radially inner and outer peripheral surfaces.
With the improved packing of this invention, the packing provides a highly desirable sealed relationship between the insert and the gland (or stuffing box), and in addition simplifies assembly of the mechanical seal into the stuffing box, particularly when the seal assembly is vertically oriented, by permitting the manual assembly of the parts while involving a secure press fit which can be manually accomplished. At the same time, the resulting press fit of the Teflon packing ring is such that distortion is greatly minimized when the packing ring is subjected to high temperature fluids, and hence leakage is believed substantially minimized.
In the improved mechanical seal assembly of this invention, the insert has a surrounding annular surface on which is sealingly seated the radially inner peripheral surface of the packing ring. This seal is created by means of a pressure or interference fit. An encircling rib is integral with the ring and projects radially outwardly therefrom, whereby the radially outer edge of this rib creates an interference fit with an annular surrounding surface formed on the gland or stuffing box. The rib is axially thin, and positioned centrally of the rectangular blocklike portion of the packing ring, and hence is effective for minimizing distortions caused by high temperatures and differential thermal expansions. The seal areas are created due to the main rectangular blocklike portion of the packing ring being axially compressed between the insert and the gland (or stuffing box), so that the seal faces are hence adjacent the axial faces of the packing, rather than the radially peripheral surfaces thereof.
Other objects and purposes of the invention will be apparent to persons familiar with apparatus of this general type upon reading the following specification and inspecting the accompanying drawings.